Because of its good thermal and electrical conductivity, copper or copper alloy is used in large quantities as an indispensable material for electric and electronic parts and heat exchanger and many other products. Its higher price than iron and its limited ore reserves necessitate, from the standpoint of effective resource usage, the recovery and recycling of its scrap produced from its use or machining. However, scrap copper cannot be recycled as such be:cause it contains a large amount of impurities such as foreign metals, solder, plating, and insulating materials. The common way of removing impurities from scrap copper is by manual separation and subsequent magnetic separation before its melting. Manual separation is limited in capacity and magnetic separation does not work on impurity elements in the form of solder, plating, or alloy components (such as Pb, Ni, Sb, S, Bi, As, Fe, Sn, and Zn). To cope with this situation, there was proposed a process for refining scrap copper by subjecting the melt of scrap copper to oxidation or reduction or to slagging by the aid of flux, thereby removing impurity elements. (Japanese Patent Publication Nos. 12409/1979 and 43094/1981 and Japanese Patent Laid-open Nos. 133125/1976, 27939/1983, 211541/1984, 226131/1984, and 217538/1986.) Improvement on this method has continued since its appearance. Of the above-mentioned methods, the one disclosed in Japanese Patent Laid-open No. 217538/1986 seems to be most effective. It consists of melting copper scrap, adding a small amount of phosphorus to the melt, performing oxidation to float impurity elements together with part of phosphorus oxide, removing residual phosphorus by oxidation while keeping the melt in a highly oxidative state, and finally removing oxygen by reduction. With this method, it is comparatively easy to remove Fe, Sn, and Zn, but it is hard to remove Pb, Ni, Sb, S, Bi, and As. Moreover, it poses a problem associated with contamination with a considerable amount of phosphorus.
The present invention was completed in view of the foregoing. It is an object of the present invention to provide a process for refining scrap copper or crude copper (called blister copper) by efficient removal of impurity elements such as Pb, Ni, Sb, S, Bi, As, Fe, Sn, and Zn in the course of melting, thereby recovering high-quality copper.